1. Field of the Invention
The present invention relates to a focus detection technique of detecting the image forming state of an object image by a lens.
2. Description of the Related Art
Conventionally, a focus detection technique based on a so-called phase difference detection scheme is known, which performs focus detection by using light beams passing through the photographing lens of a camera or the like. Various improvements and advances in this technique year by year have achieved functions convenient to users. One such improvement is to increase the number of focus detection fields. That is, the technique associated with a focus detection field, which was initially designed to focus on one middle point in the field, has been improved to increase the number of focus detection fields and also focus on peripheral points. For example, Japanese Patent Publication No. 06-001189 discloses a focus detection apparatus which has achieved a high distance measurement field density by arranging many distance measurement fields in a staggered or matrix pattern. This apparatus can focus a photographing lens at a position more suitable for an object. Japanese Patent Laid-Open No. 11-014896 discloses a focus detection apparatus designed to distribute focus detection fields uniformly at a high density from a similar viewpoint.
In order to increase the number of focus detection fields as compared with the prior art, it is necessary to reduce the size of each sensor array and increase the number of sensor arrays. This leads to disadvantages such as an increase in both circuit size and the size and cost of the photoelectric conversion element.
In addition, reducing the sensor array size leads to disadvantages such as an increase in both the difficulty and cost of the manufacturing process. Furthermore, since the area per pixel is decreased, low-luminance performance deteriorates and the line array length decreases. This leads, for example, to another disadvantage in that the defocus amount that can be measured is reduced.